JP3850101B2 - Optical disk device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk apparatus, and more particularly to an optical disk apparatus having a signal equalization function for reproducing information recorded on an optical disk such as a digital video disk (digital versatile disk) with high density without error.
[0002]
[Prior art]
In recent years, in the field of magnetic recording such as VTRs and hard disks, there is a strong demand for higher recording density, and higher density has been achieved by various techniques. However, as recording density increases, the risk of errors during recording and playback also increases, so waveform equalization processing that reduces the playback error of recorded information through signal processing of playback signals is also important. Sex is increasing. FIG. 17 is a block diagram showing a configuration of a magnetic recording signal reproducing apparatus capable of automatically performing waveform equalization of such a signal according to a conventional technique.
[0003]
In FIG. 17, reference numeral 900 denotes a magnetic recording medium on which information is recorded. Reference numeral 901 denotes a magnetic reproducing head which is brought into contact with the magnetic recording medium 900 and reads information recorded thereon. A preamplifier 902 amplifies a signal read by the head 901 and outputs a reproduction signal HF. Reference numeral 903 denotes a variable equalization filter used as equalization means, which outputs a signal QF. The equalization filter 903 determines the degree of equalization, that is, which band of the signal to be amplified with a relatively high gain, based on the control signal X output from the minimum value search means described later. Reference numeral 904 denotes a jitter measuring means that measures the jitter amount of the signal QF and outputs it as a jitter detection signal JT. Here, jitter refers to an average value or a mean square value of a deviation from a reference clock of information transition timing of a reproduction signal, and is used as an evaluation value for control as a physical quantity closely related to the above-described reproduction error rate. It is what Reference numeral 905 denotes minimum value search means for searching for the control signal X so that the jitter detection signal JT is minimized.
[0004]
First, the significance of waveform equalization when reproducing information recorded at high density will be described. It is assumed that digital information is recorded on the magnetic recording medium 900 at high density. That is, on the magnetic recording medium, digital information is recorded and held by the arrangement of the states “1” and “0”. The arrangement of “1” and “0” is basically random, and as a whole, the arrangement is in accordance with an appropriate modulation rule. However, from a partial perspective, depending on the information, a pattern in which both states alternate with a relatively short period and a pattern that alternates with a relatively long period are mixed. When such a magnetic recording is densified close to the limit of the identification resolution inherent to the magnetic head, when the magnetic head 901 scans and reproduces, each state has a short pattern. Since a phenomenon called intersymbol interference that causes interference occurs, reproduction is performed with a smaller amplitude than a portion having a long pattern. In general, the magnitude of the amplitude is directly linked to the S / N. Therefore, when a portion having a short pattern is reproduced, the S / N of the reproduced signal is deteriorated and information cannot be reproduced correctly.
[0005]
Therefore, waveform equalization is required. Assuming that the magnetic head is scanning the magnetic recording medium at a constant linear velocity, the signal reproduced from the short mark is located in the high frequency band. The variable equalization filter 903 used as equalization means restores the information signal by relatively increasing the gain of the high frequency band where the reproduction signal HF is deteriorated, and reduces the reproduction error rate. This makes it possible to compensate to some extent for the amplitude reduction due to intersymbol interference. However, if the gain is increased too much, the effect will result in a low frequency range and overall distortion of the waveform. This is a state of excessive equalization, which leads to a decrease in the quality of the reproduced signal. Thus, there is an appropriate amount for waveform equalization, and the search for the appropriate amount is automatically executed by feedback control.
[0006]
The following describes the operation of equalization processing in which such control is performed in the conventional signal reproducing apparatus configured as described above.
The magnetic reproducing head 901 reads the recorded information from the recording medium 900 and outputs it to the preamplifier 902. The preamplifier 902 amplifies the signal read by the head 901 and outputs it to the equalization means 903 as a reproduction signal HF. The equalization means performs the equalization process by increasing the gain of the high frequency component according to the control signal X, and outputs the equalization signal QF. The equalized signal QF is output from the reproducing apparatus and also output to the jitter measuring means 904 for control. The jitter measuring means 904 measures the jitter of the equalized signal QF and outputs the result to the minimum value searching means 905 as the jitter detection signal JT. The minimum value search means 905 searches for the equalization amount so that it becomes the minimum using the jitter detection signal JT as an evaluation value. As a method of searching for the optimum equalization amount, for example, the control signal X is changed by a minute amount to increase or decrease the equalization amount, and the increase / decrease in the reproduction signal jitter at that time is examined to reduce the jitter. A method of increasing or decreasing the equalization amount by changing the control signal toward the target can be used.
In the conventional magnetic recording signal reproducing apparatus, the optimum waveform equalization amount is automatically determined in this manner, and information can be reproduced from a high-density magnetic recording medium with a low error rate. (For example, Japanese Patent Publication No. 6-9340).
[0007]
[Problems to be solved by the invention]
Even in an optical disk medium that has become widespread as a large-capacity recording medium, a trend toward higher recording density is conspicuous, as symbolized by the advent of DVD, and therefore the importance of the waveform equalization technique becomes significant. .
However, in controlling the waveform equalization, when the control of the equalization amount according to the conventional technique used in the case of the magnetic recording medium as in the above example is applied to the optical disc apparatus as it is, it is not necessarily a truly optimum value. Our recent studies have shown that there may be cases where it does not converge. This will be briefly described.
[0008]
When reading a magnetic recording medium such as a magnetic disk or a tape, the head is in contact with or close to the recording medium, whereas in an optical disk apparatus, the optical head is moved to It is possible to reproduce information from the recording medium for the first time by executing focus control for correctly positioning the focal point of the convergent laser beam on the recording surface of the optical disc. Therefore, there are scanning and tracking of the medium surface and focusing for the movement of the head. Compared with the case of a magnetic recording medium only for scanning and tracking, control of the head position becomes more complicated, and further equalization processing is performed. It will also affect the control in
[0009]
When the focus control has an offset, that is, when the recording medium is irradiated at a position slightly deviated from the focus, and the so-called “out-of-focus” state is reached, the identification resolution of the head decreases and the amplitude of the high frequency component of the reproduction signal further decreases Will do. Here, it is possible to set the equalization amount so that the jitter is minimized even if the offset is maintained by applying the control according to the prior art, but in such a case, when the focus is adjusted later, the equalization amount is equal. On the contrary, a phenomenon occurs in which jitter increases and jitter increases.
[0010]
Such a phenomenon may occur when the focus position once offset returns to the original position, that is, when it is offset in the negative direction. In other words, when the head can be expected to generate a focus offset due to the expansion of the laser heat, it may have been adjusted to offset in the positive direction in advance so that the offset disappears some time after the laser is turned on. This is the case.
[0011]
Furthermore, when the equalization amount is determined by application of the conventional technique and the focus point at which the jitter becomes minimum is in the offset state, there is a problem when it is desired to search for the optimum focus position while referring to the jitter thereafter. . In other words, overcompensation occurs in the complete focus state, and jitter increases. Therefore, the focus does not converge easily and focus control becomes difficult.
[0012]
Further, there are other problems related to the characteristics of the optical disk medium. First, in use of a CD (compact disc) or a video disc, the optical disc is often used with its surface exposed. Therefore, the surface is easily damaged. Since the reproduction signal jitter is greatly disturbed by the flaw, the accuracy of the jitter minimization search is lowered due to the flaw.
[0013]
Further, the focus control is not perfect, and a focus shift easily occurs due to disturbance or impact. For example, even if the adjustment is sufficient during normal playback, if the optical head is jumped from one track to another track on the optical disc, the focus will be lost due to the impact at that time, and jitter will deteriorate momentarily. is there. In such a case, the address cannot be reproduced correctly, and a situation occurs in which the jump destination cannot be recognized and the track jump is repeated many times.
[0014]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical disc apparatus capable of accurately executing focus control and waveform equalization processing control.
It is another object of the present invention to provide an optical disc apparatus capable of reducing the influence of scratches on the optical disc medium when performing control using the jitter amount as an evaluation value.
It is another object of the present invention to provide an optical disc apparatus capable of accurately performing focus control and waveform equalization processing control even when focus disturbance such as track jump occurs. .
[0015]
[Means for Solving the Problems]
  In order to achieve the above object, an optical disc apparatus according to claim 1 is an optical disc apparatus that reads information recorded on an optical disc medium using an optical head and generates a reproduction signal. A focal position control means for controlling the focal point to a focal position set as a position in the vicinity of the information recording surface in the optical disc medium, and a set equalization amount with respect to a reproduction signal generated by the optical head An equalization unit that performs waveform equalization processing and outputs an equalization signal, a jitter measurement unit that measures the jitter of the equalization signal output from the equalization unit, and the amount of jitter is minimized.AboveEqualization amount andthe aboveFocus position andAnd an optimum value exploring means for exploring while associating with each other, the optimum value exploring means exploring a focal position where jitter is minimized within a range where the equalization amount is not overcompensated, and Amount of equalization that minimizes jitter at the focal positionIt is characterized by exploring.
[0016]
  An optical disc device according to claim 22. The optical disc apparatus according to claim 1, wherein the optimum value searching means searches for a first equalization amount that minimizes the amount of jitter at an arbitrarily set first focal position, and A second equalization amount that is less equalized than the equalization amount is obtained and set, the second equalization amount is searched for a second focal position where the amount of jitter is minimized, and A third equalization amount that minimizes the amount of jitter at the second focal position is searched.It is characterized by this.
[0017]
  An optical disk device according to a third aspect is the2. Optical disk according to 2In the deviceExecutes initial value setting that sets an insufficient equalization state as an initial value in advance.It is characterized by this.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1(Reference example)
  The optical disc apparatus according to the first embodiment of the present invention searches for the minimum jitter point with high accuracy for both the focal position and the equalization amount by using the steepest gradient method.
  FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes an optical disc (optical disc medium) on which information is recorded. An optical head 2 reads information recorded on the optical disk 1. A preamplifier 3 amplifies a signal read by the optical head 2 and outputs a reproduction signal HF. The preamplifier 3 generates a focus error signal FE along with the reproduction information signal HF. A servo amplifier 4 controls the focus position of the optical head 2. Reference numeral 5 denotes an equalization filter used as equalization means, which performs waveform equalization on the reproduction information signal HF according to the cutoff frequency Fc and outputs an equalization signal QF. A jitter measuring means 6 measures the jitter of the equalized signal QF and outputs the value as a jitter detection signal JT. Reference numeral 7 denotes minimum value search means for changing the focus position compensation signal ΔFE and the cut-off frequency Fc in a correlated manner so that the jitter detection signal JT is minimized. An adder 8 adds the focus error signal output from the preamplifier 3 and the focus position compensation signal output from the minimum value search means 7 and outputs the result to the servo amplifier 4. A spindle motor 10 rotates the optical disc 1.
[0030]
The operation of the optical disc apparatus configured as above according to the first embodiment at the time of focus position and waveform equalization control will be described below.
The optical head 2 inputs a control signal from a servo amplifier 4 to be described later to the focus actuator, thereby determining the focus position, converging the laser beam on the recording surface of the optical disc 1, and reading the recorded information. The result is output to the preamplifier 3. The preamplifier 3 amplifies the signal output from the optical head 2 and outputs the reproduction information signal HF to the equalization filter 5.
[0031]
The equalization filter 5 performs equalization processing according to a cutoff frequency Fc input from the minimum value search means 7 described later, and outputs an equalization signal QF. The equalized signal QF is output from the reproducing apparatus and is also output to the jitter measuring means 6 for control. The jitter measuring means 6 measures the jitter of the equalized signal QF and outputs the result to the minimum value searching means 7 as a jitter detection signal JT.
[0032]
The minimum value search means 7 searches the focal position and the equalization amount so as to minimize the amount of jitter obtained as the jitter detection signal JT by the steepest gradient method described later, and the focus obtained by the search. The focus compensation signal ΔFE is output to the adder 8 based on the position, and the cut-off frequency Fc is output to the equalization filter 5 based on the obtained equalization amount.
The equalization filter 5 controls the waveform equalization by using the cut-off frequency Fc for the equalization process. On the other hand, in the adder 8, the compensation signal ΔFE is added to the focus error signal FE output from the preamplifier 3, and the addition result is fed back to the focus actuator of the optical head 2 via the servo amplifier 4 to obtain the focus position. Control is executed.
[0033]
Here, the characteristics of the equalization filter 5 will be described with reference to FIG. For example, a transversal filter can be used as the equalization filter 5, but a Bessel type, an equiripple type, or the like may be used. In any case, the characteristic has a relative gain G at a specific cutoff frequency Fc as shown in FIG. 2, and either the cutoff frequency or the relative gain is input to the control signal. Anything that is correspondingly variable may be used. In the optical disc device according to the first embodiment, it is assumed that the equalization filter 5 changes the cutoff frequency Fc. In this case, since the gain of the high frequency part of the reproduction information signal HF signal can be increased by lowering the cutoff frequency Fc (Fc → Fc−ΔFc), this means that the equalization amount is increased. Conversely, by increasing the cutoff frequency (Fc → Fc + ΔFc), the equalization amount decreases, and the equalization amount can be controlled by controlling the cutoff frequency in this way.
[0034]
Next, in order to explain the search method by the minimum value search means 7, the setting of the equalization amount (cutoff frequency) and typical anti-focus / jitter characteristics corresponding to the setting will be described with reference to FIGS. Will be described. First, in FIG. 3A, when optimum equalization is performed at the cutoff frequency Fc0, the jitter is minimized at the just focus point FE0, which is a point where there is no focus shift. Even if the cutoff frequency becomes lower (→ Fc0−ΔFc: excessive equalization) or higher (→ Fc0 + ΔFc: insufficient equalization), the jitter increases. In particular, when the cut-off frequency is low and excessive equalization occurs, the anti-focus / jitter characteristic is asymmetric as shown in FIG. 3A. In such a case, there is no focus error (FE0). The jitter is not minimized, but the jitter is minimized at a slightly offset position. Also, as shown in FIG. 4, when overcompensating (excessive equalization), there are cases where jitter minimum points appear on both sides centering on the focus point. It is considered that the difference in characteristics shown in FIGS. 3 and 4 is largely caused by aberrations inherent to the optical head (spherical aberration, coma aberration, astigmatism, etc.). In any case, excessive equalization, in other words, should be optimal for signals with worse playback conditions, and if this is taken into account, the jitter may be smaller when the focus is shifted. It can be said.
[0035]
Regarding the cutoff frequency, focus position, and jitter, there is a problem because of the above relationship. When the focus position is adjusted so that the evaluation value jitter is minimized (minimum), it is true. The point that leads to the inability to find the focus point. On the other hand, even when the cutoff frequency of the equalization filter 5 is adjusted so as to minimize the jitter in a state where there is a focus offset, the state may converge to the overcompensation state (Fc0−ΔFc). is there. Therefore, it is not desirable to adjust the equalization filter and the focus independently, and it is necessary to adjust them while associating them. That is, it is necessary to simultaneously consider the cutoff frequency for the equalization filter and the focus position for focus adjustment simultaneously. FIG. 3B is a diagram showing such a relationship. A contour map is shown in which the cutoff frequency Fc shown in FIG. In the figure, the darker one indicates smaller jitter. The graph of FIG. 3 (a) is nothing but a plot of cross-sectional views at equalization filter cutoff frequencies Fc0−ΔFc, Fc0, and Fc0 + ΔFc obtained from this contour map. From this contour map, it can be seen that there is only one minimum jitter point at the intersection of the specific equalization filter cutoff frequency Fc0 and the focus position FE0. Therefore, it is necessary to perform a binary search for this combination in order to minimize the reproduction signal jitter.
[0036]
The minimum value search means 7 performs this binary search. For example, in the optical disk apparatus according to the first embodiment, the minimum value search means 7 is configured by a microprocessor, so that a somewhat complicated search method can be easily programmed. Can be realized. In the first embodiment, the minimum value search means 7 searches by the steepest gradient method.
[0037]
FIG. 5 is a diagram for explaining the steepest gradient method. Here, for simplification, the equalization filter cut-off frequency Fc is x, the focus position (which can be expressed by the focus error signal FE) is y, and the jitter JT is z. The direction vector G of the perpendicular to the contour line in FIG.
G = (∂z / ∂x, ∂z / ∂y) (1)
Can be represented. To obtain (1) specifically, x (cut-off frequency Fc) and y (focus position FE) are moved independently by a minute amount, and the jitter change amount at that time is temporarily stored and divided by each minute amount. You can do that. After that, the position of the current position (x, y) is changed to the vector ΔV, that is,
ΔV = (− ε · ∂z / ∂x, −ε · ∂z / ∂y) (2)
And move to a new coordinate (x ', y') separated by a distance. Here, ε is a constant, and can be set in advance, for example, by experimental determination.
Then, new coordinates are obtained according to the following two equations.
x ′ = x−ε · ∂z / ∂x (3)
y ′ = y−ε · ∂z / ∂y (4)
Specifically, the determination of the new coordinates is performed by the equalization filter 5 and the adder 8 with x ′ as a new value of the equalization filter cutoff frequency Fx and y ′ as the focus position compensation amount (FE + ΔFE), respectively. Will be supplied.
[0038]
Then, the new coordinates (x′y ′) obtained in (3) and (4) are newly set as (x, y), and the vectors are obtained in (1) and (2). (3), (4) If the determination of new coordinates is repeated, (x, y) converges to a point where the jitter is minimized while drawing a trajectory perpendicular to the contour line, as shown in FIG. Therefore, as a result of the search, the binary variables x and y are obtained as the equalization filter cutoff frequency FC0 at which the jitter is minimized and the focus position (which can be expressed by the focus error signal FE0).
[0039]
As described above, the optical disc apparatus according to the first embodiment includes the minimum value search means 7 for obtaining the equalization filter cutoff frequency and the focus position that minimize the jitter using the steepest gradient method. This makes it possible to accurately control the waveform equalization processing and the focus position.
[0040]
In addition, although the said thing was shown as an arithmetic expression of the steepest gradient method formula which a minimum value search means uses, the algorithm described in (2)-(4) is an example, and various deformation | transformation can be considered practically. . For example, a two-dimensional vector was obtained at once in equation (2), but the search is advanced while x (Fc) and y (FE) are slightly changed alternately and equations (3) and (4) are executed alternately. It may be.
[0041]
Embodiment 2. FIG.
The optical disc apparatus according to the second embodiment of the present invention searches for the minimum jitter point with high accuracy for both the focal position and the equalization amount by using a simple search method using two-dimensional jitter characteristics.
The optical disc apparatus according to the second embodiment of the present invention is configured in the same manner as the apparatus according to the first embodiment, and FIG. The operation of the optical disc apparatus according to the second embodiment is the same as that of the first embodiment except that the search method used by the minimum value search means 7 is different.
[0042]
Hereinafter, a simple method of binary search used in the apparatus according to the second embodiment will be described with reference to FIGS. The method described below uses the features of the contour map shown in FIG. 3 (b), and performs a search along the paths T1 to T4 shown in FIG. First, a sufficiently high value is set as an equalization filter cutoff frequency as an initial value (T0). This means that the equalization amount is set to a sufficiently small value, and is performed to simplify the search as will be described later.
[0043]
Then, in the process of T1, the equalization filter cutoff frequency is shifted by an appropriate amount to increase the equalization amount, and the change in jitter is examined. As the initial value, the cut-off frequency Fc is set to a sufficiently high setting value, and when it is gradually lowered from that point, the amount of equalization increases accordingly, so that jitter is reduced. As the exploration progresses, the jitter bottoms out and then begins to increase, the rate of change Gx turns positive. Here, for the equalization filter cut-off frequency in the first stage, an optimum value for obtaining a minimum jitter state is obtained.
At this time, the optimum Fc has been searched if it happens to be in focus, but there is a possibility that it is in an overcompensation state as described above. Therefore, next, the processes of T2 and T3 are performed, and the focus optimum value is searched as the second stage.
[0044]
In the search method used in the optical disc device according to the second embodiment, a process of shifting the filter cutoff frequency is performed so that the compensation is slightly insufficient at T2. As shown in FIG. 3 (a), the anti-focus / jitter characteristic is symmetrical only when the equalization filter is optimal or under-compensated, so that the anti-focus / jitter characteristic is symmetrical. This is to improve the accuracy of exploration. Then, in the process of T3, an optimum focus value that minimizes the jitter is searched.
[0045]
In the third stage, as the processing of T4, the search for the equalization filter cutoff frequency that minimizes the jitter again is performed using the focus position as the focus optimum value obtained in the second stage. In the third stage, a search is performed with an equalization filter cut-off frequency that becomes insufficient equalization when shifting from the first stage to the second stage as an initial value.
[0046]
FIG. 6 is a flowchart showing an algorithm of this search method by the minimum value search means 7. Steps 1 to 4 are the first stage, and the vicinity of the optimum value of the equalization filter cutoff frequency is searched. Steps 5 to 7 are the second stage, and the optimum focus value is searched. Steps 8 to 9 are the third stage, and the optimum value of the equalization filter cutoff frequency is obtained again. The operation at the time of searching in the minimum value searching means 7 of the optical disk device according to the second embodiment will be described below according to the flow of FIG.
[0047]
First, in step 1, an equalization filter cutoff frequency Fc (variable x) and a focus position (variable y) that can be expressed by the focus error signal FE are initialized. If the filter cut-off frequency is set to a sufficiently high value, the Fc search direction is fixed, so there is no need to obtain a gradient vector, and the calculation processing is simplified compared to the steepest gradient method shown in the first embodiment. Can do. On the other hand, as the initial value of the focus position, a value set to such an extent that the signal can be reproduced may be used. However, as will be described later, coarse adjustment may be performed with reference to a reproduction signal amplitude, a tracking error signal, and the like. . Any initial value can be calculated and set in advance by experiment, simulation, or the like.
[0048]
First, when step 2 is executed, the variable x is shifted to the lower side using Δx set as the change amount of the equalization filter cutoff frequency, that is, the variable x (x−Δx), and the jitter JT at that time is changed. Change (z (x, y) -z (x-Δx, y)) is measured. Then, the change rate Gx is calculated by dividing the obtained jitter change by Δx, and the positive / negative is determined. Since x is set to a sufficiently high value as an initial value, Gx becomes a negative value, and step 2 is executed after step 3. Therefore, the value of the variable x is increased by Δx until it is determined in step 2 as a positive value.
[0049]
This is a search for the above T1, and when the cut-off frequency Fc is gradually lowered from a sufficiently high set value to increase the equalization amount, the jitter is reduced accordingly. Therefore, Gx is always negative at the beginning of exploration, but when the exploration progresses and the jitter begins to bottom out and increases, the rate of change Gx turns positive. Here, step 4 is executed.
Step 4 is the process of T2 described above, and is the process of increasing x, which is the jitter minimum obtained at the stage of T1, by kΔx to make the state slightly under-compensated. As described above, this is a process for improving the asymmetry of the anti-focus / jitter characteristic so that the next focus search can be performed with high accuracy.
[0050]
Here, the relationship between symmetry and the search method will be described. In the steepest gradient method used in the first embodiment, it is necessary to obtain a differential vector as shown in the equation (2). In order to obtain this accurately, the denominator ∂y (focus offset difference) is As a result, the molecular ∂z (difference in measurement jitter) becomes small with respect to noise, resulting in a problem that a vector cannot be detected with high accuracy. On the other hand, in the exploration method according to the second embodiment, differentiation is not performed in steps 5 to 6 in the flow of FIG. 6, but only a difference in jitter when the focus offset is changed to positive or negative is obtained. . Here, since it is assumed that the anti-focus / jitter characteristic is symmetric, the fact that the jitter is equal by changing the focus by ± Δy means that the jitter is the minimum value at the point of ± 0. Accordingly, Δy at this time does not need to be a minute amount like ∂y in differentiation, but rather sufficiently larger than δ is advantageous in accuracy.
[0051]
In step 5, the variable y which is the focus is shifted by ± Δy, and a jitter change difference Gy (= z (x, y + Δy) −z (x, y−Δy)) at that time is calculated. In step 6, it is determined whether or not the absolute value of the difference Gy is equal to or less than δ. This is to determine whether or not the jitter when the focus is offset by the same amount in the opposite direction matches with an error of δ or less. If it is not less than δ in the determination of step 6, the center value of the focus offset is compensated by ε · Gy by changing the value of the variable y to y−ε · Gy (ε: constant). Repeat step 6. Steps 5 to 7 are repeated until it is determined in step 6 that it is equal to or less than δ. When it is determined in step 6 that it is equal to or less than δ, the above-described T3 ends and step 8 is executed.
[0052]
Steps 8 to 9 are T4 described above, and are the same processing as steps 2 to 3. That is, using the cut-off frequency Fc (x) set slightly under-compensated in step 4 (T2) as an initial value, a value that minimizes the jitter is searched again. If a positive value is obtained in step 8, the search ends.
In the above procedure, the equalization filter cut-off frequency, focus position changes Δx and Δy, constants k, and ε are calculated in advance by experiments, simulations, and the like, similar to the initial values of x and y. Can be set.
[0053]
As described above, in the optical disk device according to the second embodiment, the jitter is minimized by using a search method using the property that the anti-focus jitter characteristic is symmetric only when the equalization filter is optimal or under-compensated. By providing the minimum value search means 7 for obtaining the equalization filter cutoff frequency and the focus position, it is possible to accurately control the waveform equalization processing and the focus position.
[0054]
When the steepest gradient method shown in the first embodiment is applied, a binary search can be executed with high accuracy and theoretically at high speed. This is because the differential operation shown in (1) is executed with high speed and high accuracy. It is premised on what can be done. However, in practice, in order to calculate a two-dimensional partial differential, it is necessary to measure at least three points close to each other, which may cause practical problems in terms of measurement time and accuracy.
[0055]
If the initial value of the focus offset is set to a state where focus control is performed to some extent, the convergence of the subsequent search becomes faster, and the processing speed can be increased. For that purpose, the focus offset may be coarsely adjusted so that the jitter is almost minimized, but the symmetry with respect to the focus / jitter characteristic is not guaranteed by such a method. It is also possible to employ a method of adjusting the focus so that these amplitudes are maximized by using the amplitude of the reproduction information signal, the amplitude of the tracking error signal, and the like as evaluation values. A method using such other evaluation values will be described in the third embodiment.
[0056]
If the initial value of the equalization filter cut-off frequency Fc can be set to a value that is equal to or higher than the optimum frequency and is present in the vicinity of the optimum frequency, the processing in steps 1 to 4 is not necessary. Therefore, by setting such a value by experiment or simulation and using it as an initial value, it is possible to further reduce the processing load and increase the processing speed. However, optical disk media is actually an exchange medium, and the characteristics are expected to vary greatly depending on the difference in molding conditions, and it is considered difficult to set an initial value close to the optimum value without appropriate learning. According to the method using the set initial value as described above, there is a possibility that the accuracy is slightly lowered. In addition, when the focus offset optimization is performed when the initial value is extremely under-compensated, the S / N of the reproduction information signal is greatly reduced, so that sufficient accuracy may not be ensured. It is desirable to make settings.
[0057]
Embodiment 3(Reference example)
  The optical disc apparatus according to Embodiment 3 of the present invention performs focus position search and equalization amount search independently by using the amplitude of the reproduction signal or tracking error signal as an evaluation value for focus position search. is there.
  FIG. 8 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 3 of the present invention. In FIG. 8, 9 is an amplitude measuring means, which measures the amplitude of the reproduction information signal output from the preamplifier 3 and outputs an amplitude measurement signal EV. Reference numeral 72 denotes a maximum value search means, which changes the focus position compensation signal ΔFE in a correlated manner so that the amplitude measurement signal EV is maximized. The minimum value search means 71 in the second embodiment changes only the cut-off frequency Fc so as to minimize the jitter detection signal JT. The optical disk medium 1, the optical head 2, the preamplifier 3, the servo amplifier 4, the equalization filter 5, the jitter measuring means 6, the adder 8, and the spindle motor 10 are the same as those of the apparatus according to the first embodiment.
[0058]
Thus, in the apparatus according to the third embodiment, the equalization amount optimization loop involving the equalization filter 5, the jitter measurement means 6, and the minimum value search means 71, the signal amplitude measurement means 9, the maximum value search means 72, and This separates the focus position compensation loop related to the focus control loop. As described with reference to FIGS. 2 to 4, there are cases where sufficient control cannot be achieved by simply executing the signal equalization system and the focus control system independently of each other. However, this is due to the use of the same evaluation value, ie jitter, for both, and if they are controlled independently using different evaluation values, they should converge to the optimum values in each case. . Therefore, in the optical disk apparatus according to the third embodiment, the signal JT obtained from the jitter measuring means 6 is minimized in the signal equalization system, while the reproduction amplitude of the reproduction signal is maximized in the focus control system. Each exploration is performed.
[0059]
The operation of the optical disc apparatus according to the third embodiment configured as described above will be described below.
The optical head 2 determines the focus position according to the control signal from the servo amplifier 4, converges the laser beam on the recording surface of the optical disc 1, reads the recorded information, and outputs the result to the preamplifier 3. The preamplifier 3 amplifies the signal output from the optical head 2 and outputs the reproduction information signal HF to the equalization filter 5.
[0060]
The equalization filter 5 performs equalization processing according to a cutoff frequency Fc input from the minimum value search means 71 described later, and outputs an equalization signal QF. The equalized signal QF is output to the jitter measuring means 6, and the measurement result of the jitter measuring means 6 is output to the minimum value searching means 71 as the jitter detection signal JT. The minimum value search means 71 searches for an equalization amount that minimizes the amount of jitter by using a search method that will be described later, and based on the obtained equalization amount, the cutoff frequency Fc is equalized by the equalization filter 5. Output to. The equalization filter 5 controls the waveform equalization by using the cut-off frequency Fc for the equalization process.
[0061]
On the other hand, the reproduction information signal HF is also input to the amplitude measurement unit 9, and the signal amplitude measurement unit 9 measures the signal amplitude of the reproduction information signal HF and outputs the result as an amplitude measurement signal EV. As a method of measuring the amplitude by the amplitude measuring unit 9, for example, a method of full-wave rectifying the reproduction information signal HF, removing a ripple component, and outputting only a DC component can be used. The measurement result of the amplitude measuring means 9 is output as an amplitude measurement signal EV to the maximum value searching means 72, and the maximum value searching means 72 searches for a focus position that maximizes the amount of amplitude using a searching method described later. The focus compensation signal ΔFE is output to the adder 8 based on the obtained focus position. In the adder 8, the compensation signal ΔFE is added to the focus error signal FE output from the preamplifier 3, and the addition result is fed back to the focus actuator of the optical head 2 via the servo amplifier 4, and the focus position control is performed. Executed.
[0062]
Below, the search method by the minimum value search means 71 and the maximum value search means 72 is demonstrated. In our experiment, as shown in FIG. 9, when the jitter function and the amplitude function are plotted against the focus position and compared, the minimum value of the jitter function and the maximum value of the amplitude function are about 0 to 0.3 μm. It is known that the errors are almost identical. Therefore, it is considered that the focus position searched for using the signal amplitude EV as an evaluation value so as to be maximized converges in the vicinity of the position where the jitter is minimized. This exploration process is performed using the signal HF before waveform equalization, and can be executed independently without affecting the result of waveform equalization.
[0063]
The minimum value search means 71 and the maximum value search means 72 may be realized by separate microprocessors, or may be realized by a plurality of tasks in the same microprocessor. FIG. 10 is a flowchart showing a processing procedure in the minimum value searching means 71, and FIG.
In the search by the minimum value search means 71 shown in FIG. 10, steps 1 to 3 are the same as steps 1 to 3 shown in FIG. 6, and the cutoff frequency Fc (x) of the equalization filter 5 is changed from the initial value. The exploration is completed in a state where the minimum value of jitter (z) is found.
[0064]
In the search by the maximum value search means 72 shown in FIG. 11, step 1 is the same as step 1 shown in FIG. 6, and steps 2 to 4 are the same processes as steps 5 to 7 shown in FIG. Here, in the second embodiment, the purpose is to minimize the jitter (z), but in the third embodiment, the signal amplitude EV (w) is intended to be maximized. It is different in point. Therefore, when the focus position (y) is changed by a small amount (Δy), the focus position is updated so that the difference Gy of the amplitude (w) approaches 0, but the point where Gy = 0 is the minimum point. However, since it is a local maximum point, the direction of the minute displacement of the focus position made in step 4 is opposite to that in step 7 in FIG.
[0065]
Thus, in the optical disk device according to the third embodiment, the amplitude measuring means 9 for measuring the amplitude of the reproduction information signal HF and the focus position at which the amplitude is maximized are compared with the device according to the first or second embodiment. Since the maximum value searching means 72 for searching for the image is added, since the reproduction signal amplitude EV is used when performing the focus search, the focus control system and the signal equalization system are searched independently of each other. It is possible to control both with high accuracy.
[0066]
In the apparatus according to the third embodiment, both control systems are operated simultaneously, but the focus control system may be executed prior to the signal equalization system. However, it is not desirable to execute the focus control system after executing the signal equalization system first, because performing equalization control in a state where the focus is offset causes excessive equalization.
In this embodiment, the reproduction signal amplitude is used to search for the focus position. However, any signal that varies with the focus position may be used as long as the evaluation value is other than jitter. For example, if the preamplifier outputs a tracking error signal, and this is used, the same accurate control can be performed.
[0067]
Embodiment 4(Reference example)
  The optical disc apparatus according to Embodiment 4 of the present invention can accurately measure the change in jitter even if there are large and small scratches on the optical disc, avoiding or canceling them. FIG. 12 is a block diagram of the third embodiment of the present invention. In FIG. 12, the optical disc 1 is the same as that of the first embodiment, but it is assumed that a spiral track is provided on the optical disc 1 and information is recorded along this track. Reference numeral 11 denotes rotation detection means for detecting the rotation of the spindle motor 10 and generating a pulse signal RV for each rotation. Reference numeral 12 denotes a still pulse generating unit that generates a still pulse signal STL in synchronization with the pulse signal RV generated by the rotation detecting unit 11. The preamplifier 31 performs amplification similar to that of the first embodiment, but the apparatus according to the fourth embodiment outputs a tracking error signal TE together with the reproduction information signal HF. Reference numerals 32, 34, 36, and 37 denote hold means for temporarily holding the input signal. Reference numerals 33 and 44 denote adders, which add the input signals and output the addition results. Reference numerals 35 and 43 denote counters that count the input signals. Reference numeral 38 denotes a dividing unit which divides the output JY of the holding unit 36 by the output JX of the holding unit 37 and outputs the output as an average jitter signal AJT. Reference numeral 39 denotes clock generation means for generating a clock signal CK used for processing. Reference numeral 40 denotes a comparator which compares input signals and generates a control signal when a certain condition is satisfied. Reference numerals 41 and 42 denote switches that circulate the input signal to the output side in the closed state, but do not circulate the input signal to the output side in the open state. A tracking amplifier 45 outputs a control signal for controlling the optical head 2 to be positioned on a set track. The optical head 2, the equalizing filter 5, the jitter measuring means 6, and the spindle motor 10 are the same as those of the apparatus according to the first embodiment.
[0068]
The operation of the optical disc apparatus according to the fourth embodiment configured as described above will be described below. The optical head 2 determines the tracking position according to the control signal from the tracking amplifier 45, converges the laser beam on the set track on the recording surface of the optical disc 1, reads the recorded information, and sends the result to the preamplifier 3. Output. The preamplifier 3 amplifies the signal output from the optical head 2, outputs the reproduction information signal HF to the equalization filter 5, and outputs the tracking error signal TE to the adder 44. The tracking error signal TE is fed back to the tracking actuator of the optical head 2 via the tracking amplifier 45, and tracking control is executed.
[0069]
The equalization filter 5 performs equalization processing according to a cutoff frequency Fc input from a counter 43 described later, and outputs an equalization signal QF. The equalized signal QF is output to the jitter measuring means 6, and the measurement result of the jitter measuring means 6 is output to the holding means 32 as the jitter detection signal JT.
[0070]
On the other hand, the optical disk medium 1 is mounted on the spindle motor 10, and the rotation detecting means 11 generates a pulse signal RV for each rotation of the spindle motor 10. The pulse signal RV is input to the still pulse generating means 12, the counters 35 and 43, and the holding means 34, 36, and 37. The still pulse generating means 12 generates a still pulse signal STL in synchronization with the pulse signal RV, and this signal STL is further supplied to the tracking amplifier 45 via the adder 44. As a result, a track still operation is executed. That is, a one-track jump is executed in the direction opposite to the reproduction direction for each rotation, and the optical head 2 always continues to reproduce information on the same track repeatedly.
[0071]
The clock generator 39 generates a clock signal CK, and this clock signal CK is supplied to the holding means 32 and 34 and the counter 35 through the switch 41. The switch 41 is normally in a closed state and is connected in the direction in which the clock signal is output as described above. The holding means 32 temporarily holds the output signal JT of the jitter measuring means 6 according to the clock signal CK for the period of the clock signal CK, and then outputs it to the adder 33 through the switch 42. The switch 42 is normally closed, and is connected to the output of the hold means 32 to the adder 33. Reference numerals 33 and 34 respectively denote an adder and a hold means, and these function as so-called accumulators that successively add up the outputs of the hold means 32 in accordance with the clock signal CK.
[0072]
The counter 35 counts the clock signal CK. Reference numerals 36 and 37 respectively denote hold means, which temporarily hold the outputs of the hold means 34 and the counter 35 for one rotation of the spindle motor in accordance with the edge of the rotation synchronization pulse signal RV. Reference numeral 38 denotes a dividing unit which divides the output JY of the holding unit 36 by the output JX of the holding unit 37 and outputs the output as an average jitter signal AJT. The holding means 34 in which the integrated value of jitter is held is reset by the rotation synchronization pulse signal RV, whereby the initial setting for the next cycle is performed.
[0073]
FIG. 13 is a diagram for explaining tracking control and jitter measurement in the optical disc apparatus according to the fourth embodiment. Since the surface of the optical disc medium 1 is easily scratched as described above, such a scratch becomes a large error factor when measuring jitter. In the fourth embodiment, therefore, the effect of flaws can be offset by always measuring the jitter on the same track and using the integrated average of the measured jitter per track circumference.
[0074]
That is, changing the cut-off frequency Fc of the equalization filter 5 and searching for the optimum value from the increase / decrease in jitter at that time is the same as in the first to third embodiments, but the timing for switching Fc is shown in FIG. As described above, if the counter 43 is used to switch in synchronization with the rotation detection signal RV, as long as the same track is scanned, the flaw component is almost removed from the jitter increase / decrease. That is, when the cutoff frequency Fc of the equalization filter 5 is changed according to the rotation detection signal RV as shown in FIG. 13, the jitter detection signal JT is parallel as shown in FIG. Change to move. Accordingly, the jitter change amount ΔJY at this time becomes a hatched portion sandwiched between the dotted line (before the equalization filter change) and the solid line in the figure, and eventually the flaw portion is also relatively changed to cancel the influence.
[0075]
In the apparatus according to the fourth embodiment, the comparator 40 and the switches 41 and 42 are provided, so that countermeasures against larger scratches can be taken. The comparator 40 issues a control signal to open the switches 41 and 42 when the jitter detection signal JT exceeds the threshold value Vth, and serves as a flaw detection means in the apparatus of the fourth embodiment. Works.
[0076]
In FIG. 13, the integrated value Jy of jitter generated by the adder 33 and the hold means 34 is the integral of the hatched portion in the figure. If there is a large flaw in the process of generating the integrated value, the jitter increases instantaneously. In the apparatus according to the fourth embodiment, if a jitter detection signal JT exceeding a preset threshold value Jth is output, it is considered that a flaw has been detected. Thus, when there is a large flaw, the jitter detection signal JT exceeds the threshold value Vth, so that the control signal JOVR is issued from the comparator 40, so that both the switches 41 and 42 are opened.
[0077]
Accordingly, the jitter detection signal is not supplied to the adder 33 when the switch 42 is opened. Further, since the clock signal CK is not supplied to the counter 35 when the switch 41 is opened, the operation of the counter 35 is temporarily stopped. This state continues until the optical head finishes passing through the scratch and the jitter signal JT falls below the threshold value Vth. When the jitter signal JT becomes equal to or lower than the threshold value Vth, the control signal JOVR is not issued from the comparator 40, so that the switches 41 and 42 are closed again. Thereafter, the adder 33 and the holding means 34 resume the processing and continue the cumulative addition until the pulse signal RV is received. As a result, the hatched portion in the figure becomes the cumulative addition result Jy excluding the scratched portion and is held in the holding means 37.
[0078]
By dividing this by the “period” during which cumulative addition was performed, the average value can be obtained. This “period” is obtained by counting the clock signal CK with the counter 35. The count end and reset are performed according to the pulse signal RV. Further, while the signal JOVR is output, that is, during the period corresponding to the scratched part, the switch 41 is opened and the counting is interrupted. As a result, the hold circuit 36 holds the “period” Jx excluding the scratch portion. Therefore, when the integrated value Jy is divided by the period Jx, the average jitter signal AJT excluding the flaw portion is obtained.
[0079]
In the fourth embodiment, control of waveform equalization processing using jitter as an evaluation value is not mentioned and is not shown, but the equalization filter cutoff frequency Fc is controlled as in the first to third embodiments. As a result, if the average jitter signal AJT is used instead of the jitter signal JT, the influence of the flaw can be reduced and the cut-off frequency Fc can be searched with high accuracy. In the fourth embodiment, only jitter detection with respect to the cut-off frequency Fc is mentioned. However, in the case where the focus position is slightly changed for each rotation of the optical disc instead of the cut-off frequency Fc, the same as in the present embodiment. An effect can be obtained and the influence of scratches can be reduced.
[0080]
As described above, the optical disc apparatus according to the fourth embodiment includes the rotation detection unit 11, the still pulse generation unit 12, the adder 42, and the tracking amplifier 45, which make the optical head 2 the same as that of the optical disc 1. It functions as tracking control means for controlling the scanning on the track, and includes a clock generation means 39, hold means 32, 34, 36, and 37, a counter 35, and a division means 38, which are the amount of jitter. Since the average of the measured jitter per track in the same track on the optical disc 1 is obtained, the influence of scratches on the optical disc 1 can be reduced when measuring the jitter amount. It becomes possible.
[0081]
Furthermore, the optical disc apparatus according to the fourth embodiment includes a comparator 40 and switches 41 and 42, and a flaw detection unit that detects a flaw when the jitter detection signal exceeds a set threshold value. Since it functions as a calculation control means for stopping the calculation of the jitter average, it is possible to detect a large flaw and avoid its influence on the measurement.
[0082]
In the fourth embodiment, the magnitude of the jitter signal JT is used to detect a scratch on the optical disc. However, the present invention is not limited to this, and other information obtained from the reproduction signal may be used. For example, when the amplitude measuring means as shown in FIG. 8 is used, a flaw can be detected by a sharp drop in the detected amplitude.
[0083]
Embodiment 5(Reference example)
  The optical disk device according to the fifth embodiment of the present invention avoids the influence of scratches by performing a search in the inner periphery of the optical disk with few scratches.
  FIG. 14 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 5 of the present invention. Reference numeral 101 denotes an optical disc as shown in FIG. FIG. 15 will be described later. A controller 51 outputs a pulse signal for controlling the movement of the optical head 2. A flip-flop 52 outputs an H (High) or L (Low) signal corresponding to the input signal. A traverse motor 53 moves the optical head 2. A sensor 54 is located in the vicinity of the innermost periphery of the optical disc 101 and detects the optical head and outputs a signal. Reference numeral 56 denotes a sample hold circuit. In the sample state (switch-on state), the signal input from the minimum value search means 71 is circulated to the equalization filter 5, but in the hold state (switch-off state), the input signal is Distributes to the output side. The minimum value search means 71 searches for the equalization filter cutoff frequency that minimizes the jitter as in the third embodiment, but does not directly input the result of the search to the equalization filter 5, but the sample hold circuit 56. To enter. The optical head 2, the equalizing filter 5, the jitter measuring means 6, and the spindle motor 10 are the same as those of the apparatus according to the first embodiment.
[0084]
The operation of the optical disc apparatus according to the fourth embodiment configured as described above will be described below. First, the controller 51 issues a start pulse STP to set the output of the flip-flop 52 to H. When the H signal is input from the flip-flop 52, the traverse motor 53 moves the optical head 2 to the inner peripheral side of the optical disc medium 101. When the optical head 2 moves substantially to the innermost circumference of the recording surface of the optical disk medium 101, the sensor 54 detects this and outputs a flag signal D. The flag signal D is output to the flip-flop 52 and the sample hold circuit 56. The flip-flop 52 is reset when the flag signal D is input, and the output signal becomes L. Therefore, the traverse motor 53 input with this signal stops the transfer of the optical head 2.
[0085]
Then, the optimum equalization amount search by the jitter minimization method is executed by the flag signal D. That is, when the flag signal D is supplied, the sample hold circuit 56 is in the sample state, and the equalization filter cutoff frequency Fc that minimizes the jitter detection signal JT output from the jitter measuring means 6 is determined as the minimum value searching means 71. Closes the loop it explores. The equalization filter 5 receives the equalization filter cutoff frequency Fc output from the minimum value search means 71.
[0086]
Thereafter, when the drive is in a normal operation and information is reproduced, the optical head 2 moves to the outer peripheral side, so that the sensor 54 does not detect the optical head 2, so that the flag signal D is not output, The sample hold circuit 56 is in the hold state. Therefore, the equalization filter cutoff frequency Fc previously determined as a result of the minimum value search is retained thereafter, and the waveform equalization process is performed thereby.
[0087]
In other words, the above operation is nothing but the search for optimizing the equalization filter only in the innermost area of the optical disk medium. The reason for this is as follows. First, FIG. 15 shows a front view and a cross-sectional view of the optical disc medium 101 according to the fifth embodiment. An optical disk medium is often used without being put in a cartridge like a compact disk (CD) or a video disk, for example. However, when used for a long period of time, the surface of the medium is damaged as shown in FIG. As described above, these flaws not only cause errors during information reproduction, but also adversely affect optimum adjustment of the equalization filter.
[0088]
The most common type of such scratches are scratches that occur when the medium surface is rubbed with a desk or the like, that is, “scratches”. Therefore, in the fifth embodiment, as shown in FIG. 15, a protrusion 102 is provided further inside the information recording area 103 of the optical disc medium 101 so that its vicinity (innermost peripheral area) does not come into contact with a plane such as a desk. Yes. As a result, since the innermost peripheral portion is less likely to be scratched than other regions, if the optimum equalization coefficient search is performed only in the innermost peripheral region as described above, the effect of the scratch is reduced.
[0089]
As described above, the optical disk apparatus according to the fifth embodiment includes the traverse motor 53, which functions as a transport unit that transports the optical head 2 to the inner periphery with less scratches on the optical disk 101. The sensor 54, the controller 51, and A flip-flop 52 is provided, which functions as a transfer control means for controlling the transfer of the optical head, and includes a sample hold circuit 56, which performs waveform equalization according to the equalization amount searched in the innermost circumference of the optical disc 101. By functioning as an equalization amount setting means that controls so as to perform, the equalization amount searched in the innermost peripheral region with few scratches is used for waveform equalization processing, so that the influence of scratches on the optical disc 101 on the search is reduced. It becomes possible to perform control with high accuracy.
[0090]
Although the focus search is not mentioned in the fifth embodiment, it is possible to improve the accuracy of the jitter minimization. Therefore, the same effect as that of optimizing the equalization filter can be expected. That is, the effect of reducing the effect of scratches according to the fifth embodiment can be used in the search for all parameters using jitter as an evaluation amount. Further, the focus search may be configured as shown in FIG. 8 in accordance with the third embodiment, and the signal amplitude may be used as the evaluation value.
Further, by combining with the optical disk device according to the fourth embodiment, jitter can be made less susceptible to scratches by averaging the jitter for each round of the disk in the innermost peripheral region with few scratches.
[0091]
In the fifth embodiment, the sensor 54 is used to detect whether or not the optical head 2 is located on the innermost circumference. However, it is determined from the address signal or other identification signal reproduced by the optical head 2 itself. It may be determined whether or not it is on the inner circumference.
Further, in the fifth embodiment, the equalization filter set value is held based on the output of the sensor 54, but the controller 51 generates a hold signal at an appropriate timing after the end of the search without using this signal. You may do it.
[0092]
Embodiment 6(Reference example)
  The optical disc apparatus according to the sixth embodiment of the present invention uses the property that the anti-focus and jitter characteristics become gradual in an over-equalized state, thereby reducing the deterioration of jitter due to the focus fluctuation accompanying the track jump, and the address information etc. This makes it possible to detect more reliably.
  FIG. 16 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 6 of the present invention. In FIG. 16, reference numeral 61 denotes a controller, which generates a track jump command signal TJP that becomes an H (High) state at the time of track jump. The traverse motor 53 moves the optical head as in the fifth embodiment, but in the sixth embodiment, the optical head 2 is moved in the radial direction of the optical disk medium in response to a track jump command signal TJP issued from the controller 61. It is to be moved. A memory 62 stores a preset equalization filter cutoff frequency. It is assumed that the equalization filter cutoff frequency stored in the memory 62 is set as a value that causes the waveform equalization processing in the equalization filter 5 to be excessively equalized. Reference numeral 63 denotes a switch that outputs the stored contents of the memory 62 to the adder / subtracter 64 only when the switch is closed. Reference numeral 64 denotes an adder / subtracter that performs addition / subtraction calculation processing on the input signal. The optical disk medium 1, the optical head 2, the spindle motor 10, the equalization filter 5, and the jitter detection means 6 are the same as those in the first embodiment. The sample hold circuit 56 and the minimum value search means 71 are the same as those in the fifth embodiment.
[0093]
The operation of the optical disc apparatus according to the fourth embodiment configured as described above will be described below. As described above, a spiral track is provided on the recording surface of the optical disc 101, and information is recorded along this track. In the normal reproduction state, the optical head is configured to record information along the track. Reading is in progress. However, when it is necessary to read information recorded on a distant track, a track jump in which the optical head moves to the distant track instantaneously is performed.
[0094]
Without such a track jump, the track jump command signal TJP output from the controller 61 when the optical head 2 is scanning the track is L, the sample hold circuit 56 is in the sample state, and the switch 63 is opened. Suppose that At this time, the equalization filter 5, the jitter detection circuit 6, and the minimum value searching means 71 constitute a closed loop, and determine the cutoff frequency Fc so that the detected jitter value JT is minimized.
[0095]
When performing the track jump, the controller 61 issues a track jump command signal TJP (L → H), and the traverse motor 53 is activated by inputting this track jump command signal TJP, and the optical head 2 moves. Start. The track jump command signal TJP is also supplied to the sample hold circuit 56 and the switch 63. The sample hold circuit 56 enters the hold mode simultaneously with the movement of the optical head by receiving the track jump command signal TJP. Further, the switch 63 is closed by inputting the track jump command signal TJP, and the compensation value ΔFc held in the memory 62 is input to the subtractor 64. Then, the result obtained by subtracting the compensation value ΔFc from the frequency Fc input from the sample hold circuit 56 to the subtractor 64 is supplied to the equalization filter 5.
[0096]
That is, instead of the cut-off frequency Fc obtained by the search by the minimum value search means 71, Fc−ΔFc is set. As a result, the equalization signal output from the equalization filter Fc is in an excessively equalized state. Since Fc immediately before the hold has a value that minimizes the jitter, the jitter increases as Fc changes, but it is somewhat stronger against the focus disturbance caused by the vibration accompanying the movement of the optical head 2.
[0097]
This will be described with reference to FIG. When the equalization filter 5 is in the optimal equalization state (FcO), the jitter is certainly minimized at the focus optimum point (FEO), but the jitter is sharply deteriorated as the focus position shift increases. On the other hand, when the equalization filter is set to over-equalization (Fc−ΔFc), the jitter at the focus optimum point (FEO) increases, but the jitter increase due to the focus position shift is moderate, and rather a certain focus position. When there is a deviation, the jitter may be smaller than in the case of optimal equalization. In normal playback without track jump, etc., it is desirable to have minimum jitter, so if you find the optimum focus point or hold the result in a timely manner, there is no problem even if the anti-focus characteristic is steep. It will not be. However, when a track jump is executed as in the sixth embodiment, a focus shift may occur instantaneously due to vibration or impact at that time. When steady focus deviation is considered as in normal playback, it is possible to absorb this using a search method, but it is almost impossible to absorb instantaneous focus deviation within a very short time. Impossible.
[0098]
Therefore, in the sixth embodiment, the jitter in the instantaneous defocus is somewhat improved by utilizing the anti-focus jitter characteristic in the over-equalized state. That is, immediately after the track jump (TJP = L → H), the equalization filter cutoff frequency Fc that has already been optimally searched is changed from Fc−ΔFc by switching from the optimal equalization state to the overequalization state. It is none other than being. As a result, the versus-focus and jitter characteristics become a “pan bottom” as already shown in FIG. 4, and an increase in jitter can be suppressed to some extent even when the focus is greatly deviated. The reason why the sample hold circuit 56 is held by the track jump command signal TJP is to prevent the optimum search from being executed during the track jump.
[0099]
When the target address ADR to be moved by the track jump is detected and the track jump is ended, the controller 61 sets the track jump command signal TJP to L and stops the traverse motor 53. Further, when the track jump command signal becomes L, the switch 63 is opened, and the cutoff frequency used in the equalization filter 6 is returned to Fc. As a result, information reproduction can be resumed with a minimum jitter.
[0100]
As described above, the optical disc apparatus according to the sixth embodiment includes the controller 61, the switch 63, the memory 62, and the sample hold circuit 56. When there is a track jump, the switch 63, the sample hold circuit 56, Since the cut-off frequency used by the equalization filter 5 is set in advance so as to be over-equalized by switching, the vibration at the time of track jump can be obtained by using the focus / jitter characteristic at the time of over-equalization. -It is possible to suppress an increase in jitter against defocus due to impact, and as a result, it is possible to more reliably detect an address even during a track jump.
[0101]
As described above, in the sixth embodiment, a focus shift caused by a track jump is anticipated in advance, and the cut-off frequency that is optimum in a state where the focus shift exists, that is, more than the optimum frequency searched for, etc. A cut-off frequency that causes excessive conversion is set, and the set maximum cut-off frequency is used only during the track jump period. However, not only during the track jump period, it is possible to always use a cut-off frequency that is more equalized than the searched optimum frequency, which can reduce the burden on the controller and cause unexpected This makes it possible to cope with a large amount of defocusing, and in particular, when performing an operation that continuously repeats a track jump, there is an effect that the overall processing can be speeded up.
[0102]
Furthermore, by setting in this way, it is possible to cope with disc tilt caused by disc deformation or the like. In general, the disk tends to be more deformed toward the outer periphery. Therefore, as shown in the fifth embodiment, the search is performed on the innermost periphery with few scratches, and the cut-off frequency obtained by the search is calculated. When the waveform equalization processing is performed using this, there is a possibility of causing insufficient equalization at the outer peripheral portion. Therefore, by performing control so that excessive equalization is always performed, it is possible to perform good waveform equalization processing regardless of the inner and outer circumferences of the disk.
[0103]
In the sixth embodiment, the sample hold circuit 56 is set in the hold state simultaneously with the start of the track jump.
In the first to sixth embodiments, the cut-off frequency is changed to change the equalization amount, but instead, the gain G (see FIG. 2) is changed, or both are simultaneously used. Adjustment may be performed by changing the same, and the same effect can be obtained.
[0104]
In any of the embodiments, the minimum value search means and the like can be constituted by a microprocessor or the like. Since the microprocessor itself performs digital processing, the jitter signal JT as its input value or Fc, ΔFE as its output, and the focus error signal FE to be added to ΔFE are digital signals. Although it is handled as a certain thing, in any embodiment, it is not a problem at all whether it is an analog or a digital, it is only a design problem regarding the installation place of an AD converter and a DA converter. It is also possible to perform processing using an analog signal.
[0105]
【The invention's effect】
  Claim 1byAccording to the optical disc apparatus, the information recorded on the optical disc medium is read using an optical head to generate a reproduction signal, and the focal point of the light beam emitted from the optical head is recorded on the optical disc medium. Focus position control means for controlling the focus position set as a position near the surface, and a waveform equalization process using the set equalization amount for the reproduction signal generated by the optical head, and the equalization signal And a jitter measuring means for measuring the jitter of the equalized signal output from the equalizing means, and the amount of the jitter is minimized.AboveEqualization amount andAnd an optimum value exploring means for exploring the focal positions while associating them with each other, wherein the optimum value exploring means has a focal position at which jitter is minimized within a range in which the equalization amount is not overcompensated. And to find the equalization amount that minimizes jitter at the focal position.Thus, it is possible to accurately control the focus position and the waveform equalization process using the jitter amount as an evaluation value.
[0106]
  Claim 2byAccording to the optical disk device2. The optical disc apparatus according to claim 1, wherein the optimum value searching means searches for a first equalization amount that minimizes the amount of jitter at an arbitrarily set first focal position, and A second equalization amount that is less equalized than the equalization amount is obtained and set, the second equalization amount is searched for a second focal position where the amount of jitter is minimized, and A third equalization amount that minimizes the amount of jitter at the second focal position is searched.Control of the focus position and waveform equalization processing.ThanIt becomes possible to carry out with high accuracy.
[0107]
  Claim 3byAccording to an optical disc device, the claim2In the optical disk device described in the above, the optimum value searching means isSince the initial value setting for setting the under-equalization state as an initial value is executed in advance, the exploration process is simplified.It becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a diagram for explaining the operation of an equalization filter 5 of the same device.
FIG. 3 is a characteristic diagram showing a change in jitter with respect to an equalization amount and a focus position.
FIG. 4 is a characteristic diagram showing a change in jitter with respect to an equalization amount and a focus position.
FIG. 5 is a diagram for explaining the operation of the minimum value search means 7 of the same device.
FIG. 6 is a flowchart showing a processing procedure in the minimum value search of the optical disc apparatus according to the second embodiment of the present invention.
FIG. 7 is a diagram for explaining a processing procedure of the apparatus.
FIG. 8 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 3 of the present invention.
FIG. 9 is a characteristic diagram showing the relationship between jitter and amplitude.
FIG. 10 is a flowchart showing a processing procedure in the jitter minimum value search of the optical disc device according to the third embodiment of the present invention.
FIG. 11 is a flowchart showing a processing procedure in the search for the maximum amplitude value of the optical disc device according to the third embodiment of the present invention.
FIG. 12 is a block diagram showing a configuration of an optical disc apparatus according to Embodiment 4 of the present invention.
FIG. 13 is a diagram for explaining the operation of the apparatus.
FIG. 14 is a block diagram showing a configuration of an optical disc device according to a fifth embodiment of the present invention.
FIGS. 15A and 15B are a top view and a side view of an optical disc 101 used in the embodiment. FIGS.
FIG. 16 is a block diagram showing a configuration of an optical disc device according to a sixth embodiment of the present invention.
FIG. 17 is a block diagram showing a configuration of an optical disc apparatus according to a conventional technique.
[Explanation of symbols]
1,101 optical disc
2 Optical head
3,902 preamplifier
4 Servo amplifier
5,903 Equalization filter
6,904 Jitter detection means
7 Minimum value exploration means
8, 33, 40 Adder
9 Amplitude measurement means
10 Spindle motor
11 Rotation detector
12 Still pulse generation circuit
32, 34, 36, 37 Hold means
35, 43 counter
38 Division means
39 Clock generation means
40 Comparator
41, 43, 63 selector switch
45 Tracking amplifier
51, 61 controller
52 Flip-flop circuit
53 Traverse motor
54 sensors
56 Sample and hold circuit
61 controller
62 memory
71,905 Jitter minimum value search means
72 Means for searching for maximum amplitude
900 Magnetic recording medium
901 Magnetic head

Claims (3)

An optical disk device that reads information recorded on an optical disk medium using an optical head and generates a reproduction signal,
A focus position control means for controlling the focus of the light beam emitted by the optical head to a focus position set as a position in the vicinity of the information recording surface of the optical disc medium;
Equalization means for performing waveform equalization processing on the reproduction signal generated by the optical head using a set equalization amount and outputting an equalization signal;
Jitter measuring means for measuring the jitter of the equalized signal output from the equalizing means,
An optimum value search means for searching the equalization amount that minimizes the amount of jitter and the focal position while associating them with each other ,
The optimum value searching means searches for a focal position where the jitter is minimized within a range where the equalization amount is not overcompensated, and further searches for an equalization amount where the jitter is minimized at the focal position. Optical disk device. The optical disc apparatus according to claim 1 ,
The optimum value search means is:
In the first focus position set arbitrarily, and probing the first equalization amount that the amount of the jitter is minimized,
Set seeking second equalization amount to be equalized insufficient than Equalization amount of the first,
In Equalization amount of the second, to probe a second focal position where the amount of the jitter is minimized,
Further, the optical disk device comprising a Turkey to explore the third equalization amount that the amount of upper Symbol jitter is minimized Te said second focal positions odor. The optical disk apparatus according to claim 2 , wherein
The optimum value search unit, an optical disk apparatus characterized by and executes the initial value setting to set the advance equalization insufficiency as an initial value.

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